Anyone watching Alain Resnais' two masterpieces, Hiroshima Mon Amour (1959) and Last Year At Marienbad (1961), will be struck by the innovative editing, far from the so-called "invisible" techniques of classical Hollywood films.

The editor, Henri Colpi, who has died aged 84, contributed immensely to the effect of the films, which imbue the present with a constant sense of the past and the future, by rearranging or editing time. The film was the first to employ "flash-ins", abrupt interpolations of images as thoughts in the characters' minds. Indeed, if films are conceived during shooting and born in the cutting room, then Colpi was also midwife in the birth of Henri Clouzot's The Picasso Mystery (1956), Shuji Terayama's Fruits of Passion (1981), and Andrei Tarkov- sky's last film, The Sacrifice (1986), among others.

In 1982, Colpi did a superb restoration job on a lost 1920 film, L'Hirondelle et la Mesange (The Swallow And the Titmouse). André Antoine had shot six hours of film for this silent melodrama, set on two barges. However, Charles Pathé, the producer, thought it too realistic and it was never released. Colpi spliced and cut the original down to 79 minutes, the result being a fascinating look at a brilliant film from a cinematic pioneer.

The Swiss-born Colpi graduated in 1947 from the celebrated Institut des hautes Ètudes cinématographiques. From 1950 to 1960, he worked as an editor on mainly short films, including those by Georges Franju and Agnès Varda, as well as being sound editor on Resnais' moving and thought-provoking documentary Night and Fog (1955), filmed in colour in Auschwitz in the mid-1950s. The carefully controlled commentary, as well as the gentle music, contrast starkly with the intercut black and white archive material of the horrors that had taken place there not too many years before.

In 1960, Colpi began his parallel career as a director with Une aussi longue absence (The Long Absence), which won the best film award at Cannes in 1961. The poetic, poignant and beautifully underplayed film, with a screenplay by Marguerite Duras, tells of a widow (Alida Valli) who owns a cafe in a Paris suburb and meets a tramp (Georges Wilson), who may or may not be her husband who had disappeared 15 years earlier in a prison camp.

The rest of Colpi's oeuvre would never reach this quality. It was followed by two rural dramas shot in Romania, Codine (1962) and Mona: a Star without a Name (1965). "My first film, I don't know why, was considered a commercial failure. My second was a box-office flop, and my third was a huge disaster," he told Le Monde in 1985.

His directorial career was then confined to television. The exceptions were Heureux Qui Comme Ulysse (1970), a touching tale of a farmhand who escapes with his old horse to save it from being sold for bullfights, and The Mysterious Island of Captain Nemo (1973), cheaply made in Spain, co-directed with Juan Antonio Bardem, and starring Omar Sharif. Colpi, who leaves no family, was the author of two excellent books, Dèfense et Illustration de la Musique de Film (1963) and Letters to a Young Editor (1996).

· Henri Colpi, film editor and director, born July 15 1921; died January 14 2006